Hi. It's not the page wrapper specifically, the page wrapper is the element that warps the entire page. You need to expand that element to see the elements inside, and keep doing that until you get to the header, that in this case is an hgroup with the class of full-container. And then if you select that, and look at its characteristics you will notice that the margin is already 0, and what is actually taking up the space is the padding (area between the content and the border.)

Now I found when I just chose hgroup or .full-container as my selector, it had no effect because my changes were not being given priority. In order to fix this I made my selector more specific witch gave it more specificity points to give it a higher chance of being the overwriting style.

#page-wrapper > #masthead > hgroup {
padding-top: 5px;
}

I used 5px because 0 was too little white space, but you can change it to whatever you want.